Some textbook publishers also write the tests for the book. If the district wants to buy that textbook, then they also have to buy and use the publishers tests, which is usually in the contract. Teachers that write their own tests may have 3-5 different versions of the test. By not allowing the actual test to go home, the teachers can then rotate the tests that they use that year and not have to constantly be writing new tests. Since the tests don’t go home, if a student is absent for the test and needs to make it up, the teacher can use the same test without the possibility of the student knowing the questions or use an older test. The only tests that my kids got to bring home were the scantron portion of their PE tests.